"This year, for our mega 'Arrowverse' crossover, we're taking inspiration from a DC crossover from the late 1980s known as Invasion!, which featured an alien race called the Dominators, who'd previously vexed the Legion of Superheroes," Arrow and Legends of Tomorrow EP Marc Guggenheim says. "We're using cutting edge prosthetics and computer effects to achieve a feature film-quality look which is faithful to Invasion! artist Todd McFarlane's interpretation of the characters."

The Dominators are some of the more obscure DC villains, and the DC Comics blog knows that:

If you're unfamiliar with the extraterrestrial beasties, let us acquaint you. The Dominators are a sinister, technologically advanced alien race who view Earth's tendency to generate super-powered people as a sign that humans may essentially evolve to be genetically superior. So naturally, they decide to wipe us out before that ever becomes a problem.

Here are a couple images of what the Dominators looked like in their original DC comics run:

The Dominators in the original comic were part of an alliance of aliens, called the Dominion. Their connection to genetics is important, since one of the motivating factors for their invasion is the existence of the "meta-gene," a fictional gene that produces superhuman abilities. It's interesting to note that Marc Guggenheim is giving the creatures' designs special attention to keep their appearance faithful to the comics—some character designs don't age gracefully, and the little green robes and monstrous teeth may be a little too out-there compared to the visual styles of the CW series.

The crossover between The Flash, Arrow, Supergirl, and Legends of Tomorrow is expected to premiere in December. The Flash returns on Tuesday, Oct. 4, Arrow on Tuesday, Oct. 5, Supergirl on Monday, Oct. 10, and Legends of Tomorrow on Thursday, Oct. 13.